This invention relates to the operability and survivability of autonomously operated wave energy converter (WEC) buoys intended to be deployed in a body of water for an extended period of time (e.g., 2-5 years) and having a payload intended to be operational during that time.
Each autonomous WEC buoy includes a payload which requires a substantial amount of electric power for its operation. The payload is comprised of multiple different “loads” including numerous pieces of electric/electronic equipment and electro mechanical devices such as, for example (and not by way of limitation), radar and/or sonar systems, various wave and/or climate sensors, communication systems and/or relays, various control systems and associated elements, and a braking system. In order to power and operate the payload, each WEC buoy includes a system for generating (electric) power in response to wave motion, which power can then be used to operate the payload.
Any wave energy converter (WEC) device suitable for converting the forces of ocean waves into useful forms of energy and power is of interest to produce the electric power needed. In the discussion below and in the appended claims the terms “WEc buoy”, or just “buoy” and “WEC” are used interchangeably. Normally, the WEC portion of the buoy is used to power the payload and to charge, or recharge, batteries or any other suitable energy storage device for maintaining a constant supply of power to the load.
WECs are a renewable energy source, and are highly suited for use in autonomous buoy applications since they can operate without the need to re-supply the system with fuel, hydrogen or other stored energy reserves. Also, WEC buoys are of interest since wave energy has the necessary energy density for this to be feasible.
It is desirable and/or necessary for an autonomous WEC buoy and its associated equipment to remain deployed and operational for long periods of time regardless of the climatic conditions, while still providing a relatively constant electrical power to the payload. The need to provide constant electric power presents significant problems since the climatic conditions can vary greatly. At one climatic extreme, if the seas are calm (characterized by low amplitude waves) there will be little, if any, power generated. This presents a problem since the power requirements of the payload are continuous and provide a constant power drain. Thus, if the “calm” condition extends for a long period of time any energy stored will be depleted and the payload will be rendered non-operational. At the other extreme, under “storm” conditions, characterized by the amplitude of the waves exceeding a predetermined value, it is necessary to “lock-up” the buoy/WEC to prevent its destruction (ensure its survivability). In the lock-up condition the WEC produces no power. This also presents a problem since, as for the “calm” condition, certain power requirements of the payload are continuous and there is a constant power drain.
An additional problem is that the WECs typically consume a certain amount of “housekeeping” power defined as the power consumed to operate devices and equipment such as various electrical drives and rectifiers, solenoids and the like needed for the WEC to function. A problem is that for some operating conditions (e.g., low amplitude waves) the WEC consumes more power than it generates. The power consumed by the WEC for its housekeeping needs can use up all available stored energy, leaving little or none for the payload.
Still another problem relates to the deployment of a large array of WECs over an extended area of water. It is required that the WEC power delivery system operate autonomously without the need for operator intervention and be capable of providing in-situ continuous electrical power to operate sensors and relatively low power payloads.
As already noted, a problem exists in that the power generation system may not be able to provide the power to keep the batteries charged (e.g., due to adverse wave conditions; i.e., their amplitude is too low or too high) and power supplied to the payload. As a result, the equipment and devices associated with the buoy become inoperative and the status of the buoy may be compromised.
A need exists for deploying a payload which includes diverse sensing and communications equipment that can detect, track and communicate information to other sites or installations, located onshore or offshore, designed to assess the information. A WEC buoy can be used for providing power to the payload. However, a problem exists where it is extremely important that the payload remain operational for an extended period of time even when the wave conditions are such that the WEC is not generating power.